Conventional work machines such as, for example, front-end loaders, bulldozers, and excavators, may generally be powered using an internal combustion engine such as, for example, a diesel engine, a gasoline engine, or other internal combustion engine known in the art. Such internal combustion engines may emit undesirable exhaust emissions and other pollutants during operation. In recent years, and for the foreseeable future, the reduction of exhaust emissions for internal combustion engines in general and for work machines in particular, has become a regulatory priority. Furthermore, increasing fuel efficiency of vehicles and work machines has also become of increased importance, for example, to reduce increased costs associated with the rising price of fossil fuels and/or reliance on imported oil.
Driven at least in part by new and future exhaust emissions regulations and a desire to reduce fuel consumption, alternative ways to power machines have been sought. One such alternative may relate to the use of powertrains having electric components such as, for example, electric motors, generators, and electronic control systems. Such electric components have been used previously in some vehicle powertrain applications. The use of such electric components, however, in work machines in general and in work machines having ground engaging tracks in particular, may present a number of challenges not associated with other types of vehicles.
Work machines having ground engaging tracks may often be used to perform functions that require a high output torque and a relatively low maximum ground speed. Further, work machines having ground engaging tracks may often be used in environments that require extra traction and/or used for performing functions that require a high drawbar pull, for example, a drawbar pull generally in the range of about one and one-half the weight of the work machine, for performing functions such as, for example, pushing and pulling dirt. Such applications generally require a high output torque and relatively low ground speed of less than about 9 mph, for example. In addition, it may be desirable for work machines having ground engaging tracks to have an infinitely variable transmission that prevents excessive lugging of the engine, that eliminates shifting, and that reduces the need for excessive operator control while still providing an efficient powertrain system. As a result, for work machines in general and for work machines having ground engaging tracks in particular, it may be desirable to have a powertrain having a high efficiency and variable speed control in order to perform such functions.
Work machines having ground engaging tracks may often perform cycling applications. Cycling applications are applications in which the use of a work machine may require repeated starting, stopping, and reversing of direction. For example, a bulldozer may push dirt in a forward direction, stop, reverse direction, stop again, and then push dirt in the forward direction again. Another example of such cycling occurs during a typical operation of a track-type front end loader, which may repeatedly move forward while picking up a load of dirt, move in a reverse direction while carrying the load, turn, move in a forward direction while carrying the load, lift the load and dump the load into a dump truck, and reverse direction to back away from the dump truck. These exemplary cycles are often repeated many times in quick succession. As a result of such cycling applications, the kinetic energy associated with moving the work machine must be absorbed when the work machine stops. Furthermore, due to the high final drive gear ratio that may be associated with, for example, the need to have a high drawbar pull, a high amount of inertia associated with a work machine's movement may be generally reflected back to the work machine's powertrain upon stopping. Therefore, due to the typical cycling applications that may be associated with work machines having ground engaging tracks, it may be desirable to provide a work machine powertrain that is able to transfer large amounts of kinetic energy and that has a relatively low inertia to reduce the effects of inertia during cycling applications.
Work machines having ground engaging tracks may be required to operate in environments typically hostile to air-cooled machinery such as, for example, swamp-like conditions or very dusty conditions. Such conditions may render it relatively unsatisfactory to use conventional cooling systems that may rely on, for example, air filters that may quickly clog. Furthermore, air-cooled components quickly fill with dirt or mud, thereby preventing sufficient cooling and leading to premature part failure. As a result, conventional air-cooled electric components may not be suitable for use in work machines operating in these environments.
Work machines having ground engaging tracks may have a limited amount of space for placement of powertrain components. As a result, it may be desirable to use powertrain components that are relatively compact in relation to their power and/or torque output such that they have a high power density. Many conventional air-cooled electric motors, however, lack sufficient power density for use in a work machine. Therefore, it may be desirable to provide a work machine having ground engaging tracks with a powertrain having a high power density.
Work machines having ground engaging tracks may generally include one or more work implements for performing tasks associated with a particular work machine that may be operated via, for example, one or more hydraulic cylinders actuated by a hydraulic system. For example, the actuation of one or more hydraulic cylinders may be used to raise and lower the blade of a bulldozer, and/or raise and lower the bucket of a front-end loader or an excavator. Such hydraulic systems may include one or more pumps for imparting pressure to the hydraulic system. Such pumps may generally be driven via an internal combustion engine. As a result, the internal combustion engine may not only be used to propel a work machine, but it may also be used to power various work implements actuated by hydraulic cylinders. Consequently, as the demands placed on the hydraulic pump(s) are increased, for example, when a load in an excavator bucket is raised, the internal combustion engine may be called upon to provide more power, which may generally be achieved by increasing the amount of air and fuel provided to the engine to increase its engine speed.
Sometimes, however, the increase in air and fuel cannot be achieved quickly enough in response to a sudden increase in power demand for providing power to the hydraulic pump(s). This may result in the engine lugging down or stalling. In addition, when the internal combustion engine is able to sufficiently respond to the sudden hydraulic pump demand by increasing its engine speed, more exhaust emissions and less fuel efficiency may generally result. Therefore, it may be desirable to provide a system that may provide sufficient power for motive force and to operate work machine implements without lugging down or stalling the internal combustion engine and that may not result in any significant additional emissions or reduced fuel efficiency.
One tracked vehicle having internal combustion engines combined with electric motors for propulsion is described in U.S. Pat. No. 6,691,806 (the '806 patent) issued to Wolfgang et al. on Feb. 17, 2004. The '806 patent describes a drive unit for a tracked vehicle having first and second electric generators and first and second internal combustion engines driving the generators to power two pairs of first and second electric motors, with each pair of electric motors for driving a track located on one side of the vehicle. The components are wired such that if the vehicle, especially a military vehicle, is partially damaged, the vehicle can continue to move.
Although the tracked vehicle of the '806 patent includes a combination of internal combustion engines, generators, and electric motors for movement, the '806 vehicle is not a work machine and does not address the problems outlined previously herein that may be associated with work machines.
The disclosed work machine may be directed to overcoming one or more of the problems set forth above.